Site Evaluations
Lower Eightmile Creek
Site Information
Site Location:
Mt Hood NF, east of cascade crest, Forest Road 4440
Year Installed:
2000
Lat/Long:
121°26”32.90”W
45°24”47.89”N
Watershed Area (mi2):4.78
Stream Slope (ft/ft)1: 0.037
Channel Type:
Step-pool
Bankfull Width (ft): 16.5
Survey Date:
April 26 2007
1
Water surface slope extending up to 20 channel widths up and downstream of crossing.
Culvert Information
Culvert Type:
Open-bottom arch
Culvert Material:
Annular CMP
Culvert Width:
12 ft
Outlet Type:
Mitered
Culvert Length:
55 ft
Inlet Type:
Mitered
Pipe Slope (structure slope): 0.024
Culvert Bed Slope: 0.026
(First hydraulic control upstream of inlet to first hydraulic control downstream of outlet.)
Culvert width as a percentage of bankfull width: 0.73
Alignment Conditions: Appears OK. May have been slight adjustment from original stream channel.
Bed Conditions: Coarse angular material in pipe. Some material has aggraded in upstream half of
pipe. Some riprap material from inlet sides possibly being recruited into pipe.
Pipe Condition: Good condition.
Hydrology
Discharge (cfs) for indicated recurrence interval
25% 2-yr
Qbf2
2-year
5-year
10-year
50-year
100-year
43
50
171
236
287
418
478
Bankfull flow estimated by matching modeled water surface elevations to field-identified bankfull
elevations.
2
Lower Eightmile Creek
A—159
Culvert Scour Assessment
LOWER EIGHTMILE CREEK
Points represent survey points
Figure 1—Plan view map.
A—160
Lower Eightmile Creek
Site Evaluations
History
Survey Summary
There is no information available for site history.
Sixteen cross sections and a longitudinal profile
were surveyed along Lower Eightmile Creek in
April 2007 to characterize the culvert and an
upstream and downstream representative reach.
Representative sections in the culvert were taken
through a pool and steep riffle. Two additional
cross sections were surveyed upstream to
characterize the inlet as well as the contraction of
flow. Another two cross sections were surveyed
downstream of the culvert to characterize the
outlet and the expansion of flow.
Site Description
The Lower Eightmile culvert is a bottomless
arch mitered to conform to the slope of the road
fill. It is a relatively new installation (2000). The
upstream portion of the culvert is characterized
by a wide and deep pool that drops into a series
of steps/steep riffles through the culvert to the
outlet. Large angular bed material makes up
the bed through the downstream portion of the
culvert.
An upstream and downstream representative
reach were identified at this site. The upstream
representative reach consists of a series of three
wood jams that account for most of the drop
in grade through the reach. Backwater pools,
riffles, and short steps are interspersed between
the three jams. Fines have accumulated in the
backwater pools created by the jams. A low
active flood plain with large conifers and small
underbrush line both banks.
The downstream representative reach begins as
a relatively steep and evenly graded riffle. At the
downstream end, the channel opens up into a
wide backwater pool. A low flood-plain surface on
the right bank, similar to the upstream reference
reach, contributes wood to the channel. Whereas
no log jams were present in the representative
reach, large wood was present both in and
around the channel. The lack of wood jams may
be a result of the maintenance of the channel due
to its proximity to a campground area on the left
bank.
Lower Eightmile Creek
In the upstream representative reach,
representative cross sections were taken through
a pool and a riffle. An additional two sections
were taken to characterize the upstream and
downstream boundaries of the reach. In the
downstream representative reach, representative
cross sections were taken through a step and
a pool. An additional two sections were taken
to characterize the upstream and downstream
boundaries of the reach.
Profile Analysis Segment Summary
The profile analysis resulted in a total of 14 profile
segments. Two segments with similar gradient
in the upstream channel were not combined in
order to separate out the inlet transition segment
(segment I) from the upstream representative
segment K. The culvert consisted of two profile
segments. The downstream segment in the
culvert was comparable to two representative
profile segments, one in the upstream channel
and one in the downstream channel. The
upstream segment in the culvert was comparable
to one representative profile segment in the
downstream channel. The upstream transition
A—161
Culvert Scour Assessment
segment was comparable to three representative
profile segments, two in the upstream channel
and one in the downstream channel. One
downstream transition segment was comparable
to an upstream and a downstream representative
segment and one was comparable just to a
downstream representative segment. See figure
2 and table 1.
Scour Conditions
Substrate – The bed material in the pool in
the upstream portion of the culvert has more
coarse material and fewer fines than pools in the
upstream and downstream channels. This pool is
more glide-like (higher velocity and less residual
depth) than the pools in the natural channel. The
step in the culvert also has more coarse material
than the riffles/steps in the natural channel. The
D84 and D95s are both larger in the culvert than
in the riffle and step units in the natural channel.
There are also fewer fines in the culvert.
Observed conditions
Footing scour – Footings are exposed throughout
much of the culvert but they are not scoured
to the base of the footings and they generally
appear in good condition. The riprap placed
around the culvert and along the road fill has
remained in place.
Culvert-bed adjustment – There are no obvious
signs of bed adjustment except for some recently
aggraded sediment in the upstream half of
the culvert. There is angular rock forming a
step in the downstream portion of the culvert;
it is unknown whether this was placed during
construction or if it washed in from the riprap
banks at the inlet.
Profile characteristics – The profile has a convex
shape through the crossing with a rise in bed
elevation within the culvert (figure 2).
Residual depths – Culvert residual depths are
lower than residual depths in corresponding
channel segments (C, J, and A) (figure 21). The
upstream transition segment (I) has residual
depths that are both greater and less than the
range of residual depths in corresponding profile
segments (D, J, and L). The single residual depth
in downstream transition segment F is lower than
the single depth in corresponding profile segment
L.
A—162
Predicted conditions
Cross-section characteristics – Modeling
suggests that the culvert has a large effect on
flow geometry. The culvert exhibits signs of
inlet control conditions. Backwatered conditions
create subcritical flow upstream of the inlet that
transitions to supercritical or near supercritical
within the pipe. The flow geometry therefore
changes dramatically within the culvert (figures 5
through 7 and 12 through 19). Flow area, wetted
perimeter, and top width are reduced whereas
hydraulic radius and depth are increased,
particularly near the upstream end of the culvert.
Transition areas are also affected, particularly
the upstream transition (I) where widths and
depths are elevated above what is found in
corresponding profile segments in the natural
channel (D, J, and L).
Shear stress – Shear stress is low at the inlet
because of backwater effects but increases
towards the downstream end of the culvert and
is very high at the outlet area (figure 10). The
downstream transition area (F) exhibits the
greatest shear stress (figures 10 and 19). The
upstream transition (I) has low shear stress
because of the effect of culvert backwater on the
energy grade slope.
Lower Eightmile Creek
Site Evaluations
Excess shear – Model results show that the
culvert excess shear stress is within the range
of channel conditions (figure 20) except at high
flows (Q50 and above) where culvert bed mobility
may exceed that of the natural channel.
AOP Conditions
Velocity – Velocity is low at the inlet because
of backwater effects but increases towards the
downstream end of the culvert and is very high
at the outlet area (figure 11). The downstream
transition area (F) exhibits the greatest velocity
(figures 11 and 18). The upstream transition (I)
has low velocity because of the effect of culvert
backwater on the energy grade slope.
Profile complexity – Vertical sinuosity in the
culvert segments were equal to or lower than
corresponding profile segments in the natural
channel (table 4). Vertical sinuosity in the
upstream transition (I) was within the range of
corresponding profile segments (D, J, and L).
Vertical sinuosity in the downstream transition
segments (E and F) were equal to or lower than
corresponding profile segments in the natural
channel (D, L, and C).
Scour summary
Currently there are no significant signs of scour in
the pipe. The rise in bed elevation in the culvert
appears to be related to the step that makes
up the downstream half of the pipe. This step is
composed of angular large cobbles and small
boulders and may be riprap material washed
into the culvert from the banks at the inlet. There
is streambed material (rounded alluvium) that
has aggraded upstream of this step. The grade
control provided by the step, and the associated
aggradation in the upstream half of the pipe, may
be limiting culvert capacity and creating scour risk
during high flows.
Hydraulic modeling at this site indicates inlet
control conditions at high flows. High shear stress
and velocity at the downstream end of the pipe
may create scour risk. This site is a relatively
recent installation (year 2000) has not yet
experienced large flood flows. This site is likely to
experience considerable adjustment during future
floods, which may scour material from the pipe,
as well as flatten and coarsen the bed.
Lower Eightmile Creek
Cross-section complexity – The sum of squared
height differences in the culvert cross sections
are both greater than those in the channel cross
sections (table 3).
Depth distribution – The upstream cross
section in the culvert had less shallow channel
margin habitat than the natural channel but the
downstream cross-section value was within the
range of the natural channel (table 5).
Habitat units – The culvert has more glide habitat
and less pool habitat than the channel outside the
crossing (table 6).
Residual depths – Culvert residual depths are
lower than residual depths in corresponding
channel segments (C, J, and A) (figure 21). The
upstream transition segment (I) has residual
depths that are both greater and less than the
range of residual depths in corresponding profile
segments (D, J, and L). The single residual depth
in downstream transition segment F is lower than
the single depth in corresponding profile segment
L.
A—163
Culvert Scour Assessment
Substrate – The bed material in the pool in
the upstream portion of the culvert has more
coarse material and fewer fines than pools in the
upstream and downstream channels. This pool is
more glide-like (higher velocity and less residual
depth) than the pools in the natural channel. The
step in the culvert also has more coarse material
than the riffles/steps in the natural channel. The
D84 and D95 are both larger in the culvert than in
the riffle and step units in the natural channel.
There are also fewer fines in the culvert.
Large woody debris – There was a very small
amount of LWD present in the culvert (table 8).
The natural channel had moderate to very high
LWD abundance. LWD formed steps and scour
pools in the channel outside the crossing and
played a primary role in habitat unit creation and
complexity. Features in the culvert did not mimic
the role of wood in the natural channel.
AOP summary
Visual observations of the culvert bed indicate
significantly less complexity than the natural
channel bed. Large wood plays an important role
in creating steps and complexity in the natural
channel and this dynamic is not present in the
culvert. The rock step in the culvert is unlike
anything found in the natural channel. The natural
channel either has free-formed riffles of gravels
or cobbles or wood-forced steps. The complexity
metrics used in the analysis do not adequately
reflect these observations.
A—164
Flow in the culvert was wall-to-wall throughout
much of its length at the time of the survey. At low
summer flows, wide shallow flow may create fish
passage issues. At higher flows, the high velocity
in the downstream portion of the pipe may also
impede passage, especially considering the
lack of bank roughness that can provide velocity
refuge.
There were patches of exposed banks observed
during the survey but they were discontinuous
and would not create suitable conditions for
passage of terrestrial organisms at the observed
flow.
Design Considerations
Hydraulic analysis and observations at other
sample sites suggest that this site may
experience bed adjustment during future high
flows. The culvert appears to have insufficient
capacity to adequately convey high flows.
Contributing factors may include an inadequate
culvert size and the presence of aggraded
material within the pipe. Design improvements
would include a larger culvert (current culvert is
less than 75 percent of the bankfull width) and
a properly constructed bed that creates a more
uniform profile through the crossing. Constructed
bed elements could include banks that provide
flow concentration and roughness (velocity
refuge) for fish passage and that also would
provide exposed banks to facilitate passage of
terrestrial organisms.
Lower Eightmile Creek
Lower Eightmile Creek
Relative elevation (ft)
29
42
47
30
31
33
18
41
G
H
I
J
K
L
M
N
400
D
L
C
D
J
L
I
I
I
D o w n s trea m T ra n s itio n
F
F
E
C
J
A
R epres en ta tiv e
C h a n n el S eg men t
G
G
H
U ps trea m T ra n s itio n
C u lv ert S eg men t
Table 1—Segment comparisons
D
XS 3:
Pebble count
(step)
Representative Channel
XS 2:
Pebble count
(pool)
0 .0 1 3
0 .0 4 9
0 .0 4 0
0 .0 3 7
0 .0 0 6
0 .0 5 5
0 .0 2 9
0 .0 6 2
0 .0 3 7
0 .0 5 8
0 .0 2 3
XS 4
21.6%
5.6%
7.4%
0.1%
5.3%
25.9%
4.5%
28.1%
25.9%
% D ifferen c e in
G ra d ien t
Figure 2—Lower Eightmile Creek longitudinal profile.
80
85
500
13
F
XS 1
30
E
B
62
D
A
0 .0 2 8
14
C
C
0 .0 6 4
23
B
0 .0 0 7
28
A
S e g m e n t G r a d ie n t
S e g m e n t L e n g th (ft)
S egment
90 elevation (feet)
Relative
95
100
105
110
E
XS 6
XS 7:
Pebble count
(step)
G
D is ta nc e a long bed (feet)
300
XS 5
F
H
XS 9
XS 11
I
200
XS 10
XS 8:
Pebble count
(pool)
C ulvert
XS 12
J
XS 13:
Pebble count
(riffle)
K
XS 15:
Pebble count
(pool)
100
Representative Channel
XS 14
L
M
N
XS 16
0
Site Evaluations
A—165
A—166
n
o
i
t
a
v
e
l
E
)
t
f
(
F
G
H
I
J
L
0
*
5
.
1
* *
1 2 3 4 5
. . . . .
2 2 2 2 2
0.1009 – 0.1138
0.1049 – 0.1256
0.1079 – 0.1191
0.0997 – 0.1105
0.1058 – 0.1115
0.1093 – 0.1209
0.1052 – 0.1244
0.0861 – 0.1052
2
1
3
2
1
1
1
1
1
2
3
5
5
5
4
2
5
7
3
3
# of interpolated XSs
*
6
4
.
3
*
4
6
.
3
*
2
8
.
3 4
100
*
*
*
5
5
2 4 6 9 2
. . . . .
4 4 4 4 5
5
7
.
6 6 7
1
1
*
6
.
1 2
1 1
*
3 5 1
. . .
2 2 3
1 1 1
300
Main Channel Dis tance (ft)
*
3
3
3
5
3
5 8 5 7
.
. . . .
0 0
7 7 8 8 9 1 1
200
*
5
2
.
3
1
*
5
4 4
. .
3 3
1 1
4
1
*
5
.
4 5
1 1
*
3
.
5
1
5
.
5
1
*
6
.
5
1
400
*
7
.
5
1
Stations with decimal values are interpolated cross sections placed along the surveyed profile.
*
8
2
.
3
Figure 3—HEC-RAS profile.
85
90
95
100
105
110
E
115
D
0.0876 – 0.0945
0.08 – 0.0832
# of measured XSs
8
.
5
1
6
1
500
Obtained using equation from Jarrett (1984): n = 0.39S0.38R-0.16, where S=stream slope; R=hydraulic radius. Jarrett’s equation
only applied within the following ranges: S = 0.002 to 0.08, R = 0.5 ft to 7 ft. For cross sections outside these ranges, n was computed
either from adjacent sections that fell within the ranges, using the guidance of Arcement and Schneider (1987), or from the HEC-RAS
recommendations for culvert modeling.
C
1
A
SegmentRange of Manning’s n values1
Table 2—Summary of segments used for comparisons
Ground
W S Qbf
W S Q2
W S Q10
W S Q50
W S Q100
L e ge nd
Culvert Scour Assessment
Lower Eightmile Creek
Lower Eightmile Creek
Elevation (ft)
n
o
i
t
a
v
e
l
E
)
t
f
(
n
o
i
t
a
v
e
l
E
)
t
f
(
100
0
20
40
.1009
0
Station (ft)
RS = 14
Station (ft)
60
.1009
20
.11
80
40
.11
100
60
Bank St a
Ground
WS Qbf
WS Q2
WS Q10
WS Q50
WS Q100
L e ge nd
Bank St a
Ground
WS Qbf
WS Q2
WS Q10
WS Q50
WS Q100
L e ge nd
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
0
98
100
102
104
106
108
110
102
104
106
108
110
112
-20
20
.1073
0
.1049
40
.1073
60
Station (ft)
20
.1049
RS = 13
Station (ft)
RS = 15
.1073
40
.1049
80
60
100
L e ge nd
B a n k S ta
L e ve e
G ro u n d
W S Qb f
W S Q2
W S Q1 0
W S Q5 0
W S Q1 0 0
L e ge n d
Bank St a
Ground
WS Qbf
WS Q2
WS Q10
WS Q50
WS Q100
Figure 4—Cross-section plots. Only measured cross sections are included. Manning’s n values are included at the top of the cross section. The
stationing (RS) corresponds to the stationing on the HEC-RAS profile. Green arrows define the ineffective flow areas. Black arrows represent
points surveyed in as the bankfull channel boundary. Only those points identified in the field and supported by hydraulic and topographic
analyses are marked below.
Elevation (ft)
102
104
106
.1009
-20
.11
n
o
i
t
a
v
e
l
E
Elevation (ft)
108
110
112
102
-40
104
106
108
110
112
114
RS = 16
)
t
f
(
Site Evaluations
A—167
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
n
o
i
t
a
v
e
l
E
)
t
f
(
A—168
96
20
40
20
Station (ft)
60
.1079
RS = 10
Station (ft)
40
.1115
80
.1079
60
.1115
100
80
B a n k S ta
In e ff
G ro u n d
W S Qb f
W S Q2
W S Q1 0
W S Q5 0
W S Q1 0 0
L e ge n d
Bank St a
Ground
WS Qbf
WS Q2
WS Q10
WS Q50
WS Q100
L e ge nd
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
96
98
100
102
104
106
108
0
96
98
100
102
104
106
108
0
20
.1077
20
.1162
40
.1077
40
Station (ft)
RS = 9
Station (ft)
60
60
.1162
RS = 11
.1077
80
80
.1162
B a n k S ta
In e ff
G ro u n d
W S Qb f
W S Q2
W S Q1 0
W S Q5 0
W S Q1 0 0
L e ge n d
Bank St a
Ground
WS Qbf
WS Q2
WS Q10
WS Q50
100
100
L e ge nd
WS Q100
Figure 4—Cross-section plots. Only measured cross sections are included. Manning’s n values are included at the top of the cross section. The
stationing (RS) corresponds to the stationing on the HEC-RAS profile. Green arrows define the ineffective flow areas. Black arrows represent
points surveyed in as the bankfull channel boundary. Only those points identified in the field and supported by hydraulic and topographic
analyses are marked below. (continued)
Elevation (ft)
98
100
102
.1079
0
.1115
n
o
i
t
a
v
e
l
E
Elevation (ft)
104
106
108
98
-20
100
102
104
106
108
110
RS = 12
)
t
f
(
Culvert Scour Assessment
Lower Eightmile Creek
Lower Eightmile Creek
Elevation (ft)
n
o
i
t
a
v
e
l
E
)
t
f
(
n
o
i
t
a
v
e
l
E
)
t
f
(
94
-40
-20
.118
0
0
Station (ft)
.118
RS = 6
Station (ft)
.
1
1
8
20
20
40
40
60
60
B a n k S ta
In e ff
G ro u n d
W S Qb f
W S Q2
W S Q1 0
W S Q5 0
W S Q1 0 0
L e ge n d
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
-20
94
96
98
100
102
104
-40
96
98
100
102
104
106
0
-20
.1244
0
20
20
Station (ft)
.1244
RS = 5
Station (ft)
.0946
40
.
1
2
4
4
RS = 7
Note: n values for first profile.
40
60
60
L e ge nd
80
B a n k S ta
In e ff
G ro u n d
W S Qb f
W S Q2
W S Q1 0
W S Q5 0
W S Q1 0 0
L e ge n d
Bank St a
Ground
WS Qbf
WS Q2
WS Q10
WS Q50
WS Q100
Figure 4—Cross-section plots. Only measured cross sections are included. Manning’s n values are included at the top of the cross section. The
stationing (RS) corresponds to the stationing on the HEC-RAS profile. Green arrows define the ineffective flow areas. Black arrows represent
points surveyed in as the bankfull channel boundary. Only those points identified in the field and supported by hydraulic and topographic
analyses are marked below. (continued)
Elevation (ft)
96
98
100
-20
Bank St a
Ground
WS Qbf
WS Q2
WS Q10
WS Q50
WS Q100
L e ge nd
n
o
i
t
a
v
e
l
E
Elevation (ft)
102
104
106
96
-40
98
100
102
104
106
108
.0882
RS = 8
Note: n values for first profile.
)
t
f
(
Site Evaluations
A—169
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
n
o
i
t
a
v
e
l
E
)
t
f
(
A—170
88
20
.08
40
RS = 2
60
60
Station (ft)
Station (ft)
40
.08
.0861
80
80
100
Bank St a
Ground
WS Qbf
WS Q2
WS Q10
WS Q50
WS Q100
L e ge nd
100
B a n k S ta
L e ve e
G ro u n d
W S Qb f
W S Q2
W S Q1 0
W S Q5 0
W S Q1 0 0
L e ge n d
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
88
20
90
92
94
96
98
100
90
92
94
96
98
100
102
40
.0819
20
.0877
40
60
Station (ft)
.0819
RS = 1
80
Station (ft)
60
.0877
RS = 3
.0819
80
100
.0877
100
120
L e ge n d
Bank St a
Ground
WS Qbf
WS Q2
WS Q10
WS Q50
WS Q100
L e ge nd
B a n k S ta
L e ve e
G ro u n d
W S Qb f
W S Q2
W S Q1 0
W S Q5 0
W S Q1 0 0
Figure 4—Cross-section plots. Only measured cross sections are included. Manning’s n values are included at the top of the cross section. The
stationing (RS) corresponds to the stationing on the HEC-RAS profile. Green arrows define the ineffective flow areas. Black arrows represent
points surveyed in as the bankfull channel boundary. Only those points identified in the field and supported by hydraulic and topographic
analyses are marked below. (continued)
Elevation (ft)
90
92
.08
20
.0861
n
o
i
t
a
v
e
l
E
Elevation (ft)
94
96
98
0
0
100
92
94
96
98
100
102
.0861
RS = 4
)
t
f
(
Culvert Scour Assessment
Lower Eightmile Creek
Lower Eightmile Creek
.
P
.
W
l
a
t
o
T
0
50
100
150
200
250
300
0
A
50
B C
100
D
W.P. total (ft)
A—171
0
A
50
B C
Figure 6—Wetted perimeter.
10
20
30
40
50
60
70
80
100
D
Figure 5—Flow area (total) profile plot.
Flow area (sq ft)
)
t
f
(
w
o
l
F
a
e
r
A
q
s
(
)
t
f
E
E
150
150
200
Culvert
H
250
I
200
Culvert
H
250
I
Main Channel Distance (ft)
F G
Main Channel Distance (ft)
F G
300
J
300
J
K
K
350
350
L
L
M
N
400
N
Flow
400
M
Flow
450
450
W.P. Total Qbf
W.P. Total Q2
W.P. Total Q10
W.P. Total Q50
W.P. Total Q100
Legend
Flow Area Qbf
Flow Area Q2
Flow Area Q10
Flow Area Q50
Flow Area Q100
Legend
Site Evaluations
A—172
p
o
T
h
t
d
i
W
0
1
2
3
4
5
6
7
0
A
50
B C
0
0
A
50
B C
Figure 8—Top width.
Top width (ft)
20
40
60
80
100
Figure 7—Hydraulic radius.
Hydraulic radius (ft)
)
t
f
(
r
d
y
H
s
u
i
d
a
R
)
t
f
(
100
D
100
D
E
E
150
150
200
Culvert
H
250
I
200
Culvert
H
250
I
Main Channel Distance (ft)
F G
Main Channel Distance (ft)
F G
300
J
300
J
K
350
350
K
L
L
400
M
Flow
400
M
Flow
N
N
450
450
Top Width Qbf
Top Width Q2
Top Width Q10
Top Width Q50
Top Width Q100
Legend
Hydr Radius Qbf
Hydr Radius Q2
Hydr Radius Q10
Hydr Radius Q50
Hydr Radius Q100
Legend
Culvert Scour Assessment
Lower Eightmile Creek
r
a
e
h
S
n
a
h
C
q
s
/
b
l
(
100
E
E
150
F G
200
Culvert
H
250
I
300
J
J
350
K
L
L
400
M
Flow
N
N
450
Max Chl Dpth Q100
Legend
1
2
3
4
5
Lower Eightmile Creek
0
A
50
B C
100
D
Figure 10—Shear stress (channel) profile.
Shear channel (lbs/sq ft)
0
10
20
30
40
150
200
Culvert
H
250
I
Main Channel Distance (ft)
F G
Main Channel Distance (ft)
300
350
K
400
M
Flow
450
Shear Chan Qbf
Shear Chan Q2
Shear Chan Q10
Shear Chan Q50
Shear Chan Q100
Legend
Max Chl Dpth Qbf
Max Chl Dpth Q2
Max Chl Dpth Q10
50
D
6
0
B C
Max Chl Dpth Q50
A
7
8
9
Figure 9—Maximum depth.
Maximum channel depth (ft)
)
t
f
x
a
M
l
h
C
h
t
p
D
)
t
f
(
Site Evaluations
A—173
)
s
/
t
f
(
A—174
l
e
V
l
n
h
C
0
0
50
100
Figure 11—Velocity (channel) profile plot.
Velocity channel (ft/s)
2
4
6
8
10
12
150
250
Main Channel Distance (ft)
200
300
350
400
450
Vel Chnl Qbf
Vel Chnl Q2
Vel Chnl Q10
Vel Chnl Q50
Vel Chnl Q100
Legend
Culvert Scour Assessment
Lower Eightmile Creek
Flow area (ft2)
A—175
J
L A C D
A
L
J
G (Culv)
H (Culv)
F (DS Trans)
Qbf
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
E (DS Trans)
D
A C D
I (US Trans)
Figure 12—Flow area (total).
0
50
A
100
Flow Area (ft2)
150
200
250
300
50%
of the
values
A
L
I (US Trans)
J
H (Culv)
E (DS Trans)
F (DS Trans)
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
G (Culv)
2
D
J L A C D
100%
of the
values
G (Culv)
H (Culv)
E (DS Trans)
F (DS Trans)
C
J
L A C D
Minimum value
25th percentile
10
J L A C D
A
L
J
H (Culv)
E (DS Trans)
F (DS Trans)
50
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
G (Culv)
Median (aka 50th percentile)
75th percentile
Maximum value
A
L
J
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
I (US Trans)
Box Plot Explanation
I (US Trans)
D
C
Lower Eightmile Creek
C
L
L
I (US Trans)
J
G (Culv)
H (Culv)
E (DS Trans)
F (DS Trans)
100
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
J
Site Evaluations
D
C
D
C
H (Culv)
A C D
C
C
G (Culv)
H (Culv)
G (Culv)
J
J
L A C D
2
H (culv)
G (culv)
I (us trans)
F
(ds
trans)
E (ds trans)
F (DS Trans)
F (DS Trans)
F (DS Trans)
Qbf
D
D
A C D
E (DS Trans)
E (DS Trans)
F (DS Trans)
2
H (Culv)
L
J
L
J L
H (Culv)
I (US Trans)
A
A
H (culv)
G (culv)
I (us trans)
F
(ds
trans)
E (ds trans)
I (US Trans)
Figure 14—Hydraulic radius.
0
I (US Trans)
J
E (DS Trans)
Hydraulic
Radius (ft)
1
2
3
4
5
6
7
G (Culv)
G (Culv)
Qbf
10
L A C D
J L A C D
10
H (culv)
G (culv)
I (us trans)
F
(ds
trans)
E (ds trans)
G (Culv)
L
L
F (DS Trans)
F (DS Trans)
A
A
G (Culv)
H (Culv)
A
A
C
C
J
H (culv)
G (culv)
I (us trans)
F
(ds
trans)
E (ds trans)
H (Culv)
I (US Trans)
H (culv)
G (culv)
I (us trans)
F
(ds
trans)
E (ds trans)
I (US Trans)
J
C
C
D
D
L
L
H (culv)
G (culv)
I (us trans)
F
(ds
trans)
E (ds trans)
E (DS Trans)
E (DS Trans)
A
A
J L
J
A C D
50
A C D
50
H (culv)
G (culv)
I (us trans)
F
(ds
trans)
E (ds trans)
J L
H (culv)
G (culv)
I (us trans)
F
(ds
trans)
E (ds trans)
F (DS Trans)
F (DS Trans)
J
H (Culv)
A C D
H (Culv)
I (US Trans)
J L
I (US Trans)
J
D
D
C
C
G (Culv)
G (Culv)
I (US Trans)
J
Figure 13—Wetted perimeter.
Hydraulic Radius (ft)
E (DS Trans)
D
D
L
L
J L A C D
E (DS Trans)
E (DS Trans)
A
A
A C D
D
D
0
J
L
L
J
H (Culv)
100
L
100
H (culv)
G (culv)
I (us trans)
F
(ds
trans)
E (ds trans)
J
H (culv)
G (culv)
I (us trans)
F
(ds
trans)
E (ds trans)
G (Culv)
20
Wetted Perimeter (ft)
C
C
F (DS Trans)
F (DS Trans)
40
E (DS Trans)
E (DS Trans)
G (Culv)
H (Culv)
60
I (US Trans)
I (US Trans)
A—176
J
Wetted perimeter (ft)
L
80
Culvert Scour Assessment
Lower Eightmile Creek
H (Culv)
I (US Trans)
H (Culv)
G (Culv)
Qbf
F (DS Trans)
F (DS Trans)
F (DS Trans)
J
J
L A C D
2
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
H (Culv)
J
L
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
A
F (DS Trans)
G (Culv)
A
A C D
H (Culv)
I (US Trans)
L
J L
I (US Trans)
J
D
A C D
I (US Trans)
J
Figure 16—Maximum depth.
0
C
C
L
L
E (DS Trans)
2
Maximum Depth (ft)
4
6
8
D
D
A
A
G (Culv)
Figure 15—Top width.
E (DS Trans)
E (DS Trans)
G (Culv)
2
D
D
J
J
L A C D
10
10
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
J L A C D
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
G (Culv)
Qbf
C
C
F (DS Trans)
F (DS Trans)
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
E (DS Trans)
E (DS Trans)
G (Culv)
H (Culv)
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
H (Culv)
I (US Trans)
A C D
I (US Trans)
J
J L
C
C
L
L
J L
J
A C D
50
A C D
50
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
J L
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
F (DS Trans)
F (DS Trans)
J L A C D
H (Culv)
A
A
G (Culv)
G (Culv)
A C D
H (Culv)
I (US Trans)
0
I (US Trans)
J
15
D
D
L
L
45
E (DS Trans)
E (DS Trans)
A
A
60
D
D
75
J
L
L
J
100
L
100
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
J
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
G (Culv)
90
C
C
F (DS Trans)
F (DS Trans)
A
A
E (DS Trans)
E (DS Trans)
G (Culv)
H (Culv)
C
C
H (Culv)
I (US Trans)
30
Top Width (ft)
Maximum depth (ft)
D
I (US Trans)
J
Lower Eightmile Creek
L
Top width (ft)
E (DS Trans)
Site Evaluations
A—177
G (Culv)
I (US Trans)
I (US Trans)
H (Culv)
H (Culv)
F (DS Trans)
F (DS Trans)
H (culv)
G (culv)
I (us trans)
F
(ds
trans)
E (ds trans)
G (Culv)
Qbf
E (DS Trans)
J L
A C D
2
H (culv)
G (culv)
I (us trans)
F
(ds
trans)
E (ds trans)
E (DS Trans)
C
C
J L A C D
H (Culv)
H (Culv)
E (DS Trans)
E (DS Trans)
A C D
G (Culv)
G (Culv)
J
J
Figure 18—Velocity (channel).
0
I (US Trans)
I (US Trans)
D
Velocity
3 (ft/sec)
6
9
12
D
D
J
J
L
L
Figure 17—Width-to-depth ratio.
2
C
C
A
A
F (DS Trans)
F (DS Trans)
Qbf
10
J
L A C D
J
L A C D
10
H (culv)
G (culv)
I (us trans)
F
(ds
trans)
E (ds trans)
F (DS Trans)
L
L
F (DS Trans)
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
E (DS Trans)
E (DS Trans)
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
H (Culv)
H (Culv)
A
A
G (Culv)
G (Culv)
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
I (US Trans)
I (US Trans)
A C D
D
D
J
J
J L
C
C
L
L
J L
A C D
50
A C D
50
H (culv)
G (culv)
I (us trans)
F
(ds
trans)
E (ds trans)
J L
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
F (DS Trans)
F (DS Trans)
J L A C D
E (DS Trans)
E (DS Trans)
A C D
H (Culv)
H (Culv)
A
A
G (Culv)
G (Culv)
0
I (US Trans)
I (US Trans)
20
D
D
J
J
30
C
C
40
D
D
L
L
J
L
L
J
100
L
100
H (culv)
G (culv)
I (us trans)
F
(ds
trans)
E (ds trans)
J
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
F (DS Trans)
F (DS Trans)
A
A
E (DS Trans)
E (DS Trans)
C
C
H (Culv)
H (Culv)
A
A
G (Culv)
G (Culv)
10
Width-to-depth Ratio
Velocity (ft/sec)
D
I (US Trans)
I (US Trans)
A—178
J
Width-to-depth ratio
L
50
Culvert Scour Assessment
Lower Eightmile Creek
Shear stress (lbs/ft2)
A C D
L
I (US Trans)
J
G (Culv)
H (Culv)
F (DS Trans)
Qbf
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
Excess shear (Applied/tcrit)
D
C
A
200
300
C
Dis charge (cfs )
G (Culv)
F (DS Trans)
2
I (US Trans)
H (Culv)
500
600
I (US Trans)
J
G (Culv)
H (Culv)
E (DS Trans)
F (DS Trans)
L A C D
10
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
J
L
D
C
L
J
D
size. Values of excess shear greater than 1 indicate bed movement for the D84 particle size.
Figure 20—Excess shear stress.
C
DS Channel (US pebble count) - step
Culvert (DS pebble count) - step
US Channel (DS pebble count) - riffle
A C D
A
Excess shear stress is the channel shear divided by the critical shear for bed entrainment of the D84 particle
Excess Shear (Applied / tcrit)
0
0
100
2
4
6
8
J L
A
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
E (DS Trans)
400
J L A C D
A
Figure 19—Shear stress (channel).
0
E (DS Trans)
Lower Eightmile Creek
10
Shear Stress (lbs/ft2)
20
30
40
A C D
A
L
I (US Trans)
J
G (Culv)
H (Culv)
E (DS Trans)
F (DS Trans)
50
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
J L
L
L
I (US Trans)
J
G (Culv)
H (Culv)
E (DS Trans)
F (DS Trans)
100
H (culv)
G (culv)
I (us trans)
F (ds
trans)
E (ds
trans)
J
Site Evaluations
A—179
D
C
D
Culvert Scour Assessment
Table 3—Sum of squared height difference
Reach
XSUnit type
Location
Culvert
Sum of squared
height difference
Within range of
channel conditions?
US
Pool
0.09
No
DS
Step
0.10
No
US
Pool
0.04
DS
Riffle
0.08
US
Step
0.06
DS
Pool
0.05
Upstream
Downstream
Table 4—Vertical sinuosity
Segment
A
DS channel
1.001
B
DS channel
1.000
C
DS channel
1.009
D
DS channel
1.001
E
DS transition
1.004
F
DS transition
1.001
G
Culvert
1.007
H
Culvert
1.001
I
US transition
1.003
J
US channel
1.012
K
US channel
1.009
L
US channel
1.004v
M
US channel
1.005
N
US channel
1.003
A—180
LocationVertical Sinuosity (ft/ft)
Lower Eightmile Creek
Site Evaluations
Table 5—Depth distribution
Reach
XS Location
25% Q2
Culvert
Within range of
channel conditions?
US
0
No
DS
3
Yes
US
8
DS
3
US
1
DS
8
Upstream
Downstream
Table 6—Habitat unit composition
Percent of surface area
Reach
Pool Glide
Riffle
Step
Culvert
12%
47%
33%
0%
Upstream Channel
70%
4%
12%
14%
Downstream Channel
32%
0%
53%
15%
1.2
Residual Depth (ft)
1.0
0.8
0.6
0.4
Residual depth (ft)
0.2
Segment N
Segment M
Segment L
Segment K
Segment J
Segment I
US Transition
Segment H
Culvert
Segment G
Culvert
Segment F
DS Transition
Segment E
DS Transition
Segment D
Segment C
Segment B
Segment A
0.0
Culvert Culvert
Segment Segment
J
Segment
L
SegmentSegment
A
Segment
B
Segment
C
D
K
Segment
N
Segment
M
Segment
H:Transition
Segment
G:
Segment
Segment
E: DS Transition
F:
DS Transition
Segment I: US
Figure 21­—Residual depths.
Lower Eightmile Creek
A—181
Culvert Scour Assessment
Table 7—Bed material sorting and skewness
Reach
XSUnit
Sorting
Location
Type
Culvert
Within range Skewness
of channel
conditions?
Within range
of channel
conditions?
US
Pool
2.27
Yes
0.26
Yes
DS
Step
1.22
No
-0.15
No
US
Pool
2.06
0.35
DS
Riffle
3.17
0.36
US
Step
1.59
0.35
DS
Pool
2.64
0.00
Upstream
Downstream
Table 8—Large woody debris
Reach
Culvert
Pieces/Channel
Width
0.3
Terminology:
US = Upstream
DS = Downstream
Upstream
5.49
RR = Reference reach
Downstream
1.73
XS = Cross section
View upstream through culvert.
A—182
View downstream through culvert.
Lower Eightmile Creek
Site Evaluations
Downstream reference reach - upstream
Downstream reference reach – downstream
pebble count, riffle. pebble count, pool.
Upstream reference reach – upstream
pebble count, pool. Upstream reference reach – downstream
pebble count, riffle.
Culvert – downstream pebble count, riffle.
Lower Eightmile Creek
Culvert – upstream pebble count, pool.
A—183
Culvert Scour Assessment
Cross section: Upstream Reference Reach – Upstream Pebble Count
Material
sand
very fine gravel
fine gravel
fine gravel
medium gravel
medium gravel
coarse gravel
coarse gravel
very coarse gravel
very coarse gravel
small cobble
medium cobble
large cobble
very large cobble
small boulder
small boulder
medium boulder
large boulder
very large boulder
bedrock
S ize C las s (mm)
C ount
Item %
C umulative %
35
4
1
2
8
13
10
15
5
5
1
0
1
0
0
0
0
0
0
0
35%
4%
1%
2%
8%
13%
10%
15%
5%
5%
1%
0%
1%
0%
0%
0%
0%
0%
0%
0%
35%
39%
40%
42%
50%
63%
73%
88%
93%
98%
99%
99%
100%
100%
100%
100%
100%
100%
100%
100%
<2
2-4
4 - 5.7
5.7 - 8
8 - 11.3
11.3 - 16
16 - 22.6
22.6 - 32
32 - 45
45 - 64
64 - 90
90 - 128
128 - 180
180 - 256
256 - 362
362 - 512
512 - 1024
1024 - 2048
2048 - 4096
Bedrock
40
100%
35
90%
Frequency
70%
25
60%
20
50%
40%
Frequency
15
30%
10
20%
5
Cumulative Frequency
10%
Bedrock
2048-4096
512-1024
1024-2048
362-512
256-362
180-256
128-180
64-90
90-128
45-64
32-45
22.6-32
16-22.6
8-11.3
11.3-16
5.7-8
<2
4-5.7
<2
0%
2-4
0
2-4
4 - 5.7 - 8
32 -45
45-64
64- 90
8 - 11.3
90 - 128
Bedrock
11.316- 16
-22.6
22.6- 32
128180
- 180
256
- 256
362
- 362
- 512
512 - 1024
Particle Size Category (mm)
1024
2048
- 2048
- 4096
Particle Size Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
1
1
12
28
50
140
A—184
Cumulative Frequency
80%
30
Sorting Coefficient:
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
35%
63%
2%
0%
0%
2.06
Skewness Coefficient: 0.35
Lower Eightmile Creek
Site Evaluations
Cross section: Upstream Reference Reach – Downstream Pebble Count
Material
sand
very fine gravel
fine gravel
fine gravel
medium gravel
medium gravel
coarse gravel
coarse gravel
very coarse gravel
very coarse gravel
small cobble
medium cobble
large cobble
very large cobble
small boulder
small boulder
medium boulder
large boulder
very large boulder
bedrock
S ize C las s (mm)
C ount
Item %
C umulative %
16
1
1
1
1
3
4
10
8
7
5
8
8
7
4
0
4
0
0
0
18%
1%
1%
1%
1%
3%
5%
11%
9%
8%
6%
9%
9%
8%
5%
0%
5%
0%
0%
0%
18%
19%
20%
22%
23%
26%
31%
42%
51%
59%
65%
74%
83%
91%
95%
95%
100%
100%
100%
100%
<2
2-4
4 - 5.7
5.7 - 8
8 - 11.3
11.3 - 16
16 - 22.6
22.6 - 32
32 - 45
45 - 64
64 - 90
90 - 128
128 - 180
180 - 256
256 - 362
362 - 512
512 - 1024
1024 - 2048
2048 - 4096
Bedrock
100%
16
90%
14
80%
70%
Frequency
12
60%
10
50%
8
Frequency
6
40%
30%
Bedrock
2048-4096
1024-2048
362-512
512-1024
256-362
180-256
90-128
128-180
64-90
45-64
32-45
22.6-32
Cumulative Frequency
2-4
4 - 5.7 - 8
32 -45
45-64
64- 90
8 - 11.3
90 - 128
Bedrock
11.316- 16
-22.6
22.6- 32
128180
- 180
256
- 256
362
- 362
- 512
Particle Size Category (mm)
512 - 1024
1024
2048
- 2048
- 4096
Particle Size Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
1
1
43
200
313
530
Lower Eightmile Creek
11.3-16
<2
16-22.6
0%
5.7-8
0
8-11.3
10%
4-5.7
2
<2
20%
2-4
4
Cumulative Frequency
18
Sorting Coefficient:
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
18%
41%
32%
9%
0%
3.17
Skewness Coefficient: 0.36
A—185
Culvert Scour Assessment
Cross section: Culvert – Upstream Pebble Count
Material
sand
very fine gravel
fine gravel
fine gravel
medium gravel
medium gravel
coarse gravel
coarse gravel
very coarse gravel
very coarse gravel
small cobble
medium cobble
large cobble
very large cobble
small boulder
small boulder
medium boulder
large boulder
very large boulder
bedrock
S ize C las s (mm)
<2
2-4
4 - 5.7
5.7 - 8
8 - 11.3
11.3 - 16
16 - 22.6
22.6 - 32
32 - 45
45 - 64
64 - 90
90 - 128
128 - 180
180 - 256
256 - 362
362 - 512
512 - 1024
1024 - 2048
2048 - 4096
Bedrock
C ount
Item %
C umulative %
9
1
0
5
7
8
10
3
2
10
13
14
6
6
6
0
0
0
0
0
9%
1%
0%
5%
7%
8%
10%
3%
2%
10%
13%
14%
6%
6%
6%
0%
0%
0%
0%
0%
9%
10%
10%
15%
22%
30%
40%
43%
45%
55%
68%
82%
88%
94%
100%
100%
100%
100%
100%
100%
16
100%
14
90%
Frequency
70%
10
60%
8
50%
40%
Frequency
6
30%
4
20%
Bedrock
2048-4096
1024-2048
362-512
512-1024
256-362
180-256
90-128
128-180
64-90
45-64
32-45
22.6-32
11.3-16
Cumulative Frequency
2-4
4 - 5.7 - 8
32 -45
45-64
64- 90
8 - 11.3
90 - 128
Bedrock
11.316- 16
-22.6
22.6- 32
180
- 180
256
- 256
362
- 362
- 512
Particle Size Category 128
(mm)
512 - 1024
1024
2048
- 2048
- 4096
Particle Size Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
1
10
50
180
262
330
A—186
16-22.6
5.7-8
<2
8-11.3
0%
4-5.7
0
<2
10%
2-4
2
Cumulative Frequency
80%
12
Sorting Coefficient:
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
9%
46%
39%
6%
0%
2.27
Skewness Coefficient:0.26
Lower Eightmile Creek
Site Evaluations
Cross section: Culvert – Downstream Pebble Count
Material
sand
very fine gravel
fine gravel
fine gravel
medium gravel
medium gravel
coarse gravel
coarse gravel
very coarse gravel
very coarse gravel
small cobble
medium cobble
large cobble
very large cobble
small boulder
small boulder
medium boulder
large boulder
very large boulder
bedrock
S ize R ange (mm)
C ount
Item %
C umulative %
0
0
0
0
0
1
2
2
3
10
16
18
7
7
12
8
6
0
0
0
0%
0%
0%
0%
0%
1%
2%
2%
3%
11%
17%
20%
8%
8%
13%
9%
7%
0%
0%
0%
0%
0%
0%
0%
0%
1%
3%
5%
9%
20%
37%
57%
64%
72%
85%
93%
100%
100%
100%
100%
<2
2-4
4 - 5.7
5.7 - 8
8 - 11.3
11.3 - 16
16 - 22.6
22.6 - 32
32 - 45
45 - 64
64 - 90
90 - 128
128 - 180
180 - 256
256 - 362
362 - 512
512 - 1024
1024 - 2048
2048 - 4096
> 4096
100%
20
80%
Frequency
16
14
60%
12
40%
10
8
Frequency
6
20%
4
Cumulative Frequency
18
0%
Cumulative Frequency
2
Bedrock
2048-4096
1024-2048
362-512
512-1024
256-362
180-256
128-180
64-90
90-128
45-64
32-45
22.6-32
16-22.6
11.3-16
5.7-8
8-11.3
<2
4-5.7
<2
-20%
2-4
0
2-4
4 - 5.7
5.7 - 8
> 4096
32 -45
45-64
64- 90
8 - 11.3
90 - 128
11.316
- 16
-22.6
22.6- 32
128180
- 180
256
- 256
362
- 362
- 512
512
1024
Particle Size Category (mm)
1024
2048
- 2048
- 4096
Particle Size Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
36
60
120
350
525
550
Lower Eightmile Creek
Sorting Coefficient:
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
0%
20%
52%
28%
0%
1.22
Skewness Coefficient:-0.15
A—187
Culvert Scour Assessment
Cross section: Downstream Reference Reach – Upstream Pebble Count
Material
sand
very fine gravel
fine gravel
fine gravel
medium gravel
medium gravel
coarse gravel
coarse gravel
very coarse gravel
very coarse gravel
small cobble
medium cobble
large cobble
very large cobble
small boulder
small boulder
medium boulder
large boulder
very large boulder
bedrock
S ize C las s (mm)
C ount
Item %
C umulative %
2
0
1
1
2
4
4
1
6
6
8
8
16
13
16
9
1
0
0
0
2%
0%
1%
1%
2%
4%
4%
1%
6%
6%
8%
8%
16%
13%
16%
9%
1%
0%
0%
0%
2%
2%
3%
4%
6%
10%
14%
15%
21%
28%
36%
44%
60%
73%
90%
99%
100%
100%
100%
100%
<2
2-4
4 - 5.7
5.7 - 8
8 - 11.3
11.3 - 16
16 - 22.6
22.6 - 32
32 - 45
45 - 64
64 - 90
90 - 128
128 - 180
180 - 256
256 - 362
362 - 512
512 - 1024
1024 - 2048
2048 - 4096
Bedrock
100%
16
90%
80%
Frequency
14
70%
12
60%
10
50%
8
Frequency
6
40%
30%
4
20%
2
10%
Cumulative Frequency
Bedrock
2048-4096
512-1024
1024-2048
362-512
256-362
180-256
128-180
64-90
90-128
45-64
32-45
22.6-32
16-22.6
8-11.3
11.3-16
5.7-8
<2
4-5.7
<2
0%
2-4
0
Cumulative Frequency
18
2-4
4 - 5.7
5.7 - 8
32 -45
45-64
64- 90
8 - 11.3
90 - 128
Bedrock
11.316- 16
-22.6
22.6- 32
128180
- 180
256
- 256
362
- 362
- 512
512 - 1024
Particle Size Category (mm)
1024
2048
- 2048
- 4096
Particle Size Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
10
35
140
300
420
550
A—188
Sorting Coefficient:
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
2%
26%
46%
27%
0%
1.59
Skewness Coefficient: 0.35
Lower Eightmile Creek
Site Evaluations
Cross section: Downstream Reference Reach – Downstream Pebble Count
Material
sand
very fine gravel
fine gravel
fine gravel
medium gravel
medium gravel
coarse gravel
coarse gravel
very coarse gravel
very coarse gravel
small cobble
medium cobble
large cobble
very large cobble
small boulder
small boulder
medium boulder
large boulder
very large boulder
bedrock
S ize C las s (mm)
C ount
Item %
C umulative %
32
4
3
7
6
4
5
10
11
6
3
0
2
0
4
0
2
0
0
0
32%
4%
3%
7%
6%
4%
5%
10%
11%
6%
3%
0%
2%
0%
4%
0%
2%
0%
0%
0%
32%
36%
39%
46%
53%
57%
62%
72%
83%
89%
92%
92%
94%
94%
98%
98%
100%
100%
100%
100%
<2
2-4
4 - 5.7
5.7 - 8
8 - 11.3
11.3 - 16
16 - 22.6
22.6 - 32
32 - 45
45 - 64
64 - 90
90 - 128
128 - 180
180 - 256
256 - 362
362 - 512
512 - 1024
1024 - 2048
2048 - 4096
Bedrock
100%
35
80%
Frequency
25
70%
60%
20
50%
15
Frequency
40%
30%
10
20%
5
Cumulative Frequency
10%
Bedrock
2048-4096
1024-2048
362-512
512-1024
256-362
180-256
128-180
64-90
90-128
45-64
32-45
22.6-32
11.3-16
16-22.6
5.7-8
8-11.3
2-4
<2
4-5.7
0%
<2
0
2-4
4 - 5.7 - 8
32 -45
45-64
64- 90
8 - 11.3
90 - 128
Bedrock
11.316- 16
-22.6
22.6- 32
128180
- 180
256
- 256
362
- 362
- 512
512 - 1024
Particle Size Category (mm)
1024
2048
- 2048
- 4096
Particle Size Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
1
1
10
50
271
700
Lower Eightmile Creek
Cumulative Frequency
90%
30
Sorting Coefficient:
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
32%
57%
5%
6%
0%
2.64
Skewness Coefficient: 0.00
A—189